There are two separate concepts here. One is MS voices/speech-engine (Anna vs Zira), which can be used by any program. The other is Siri/Cortana/GoogleNow interfaces that make use of speech functionality.

Just give it a little bit more time. The only thing holding back voice interaction on computers has been the quality of the computer's voice, and the recognition software. Both of these has improved dramatically over the last couple of years. I think it's only a matter of time before talking to your PC is the norm.